Research Of Mutual Coupling Reduction Of MIMO Antenna Arrays Based On Metasurface

With the development of the fifth-generation(5G)wireless communication systems,Massive-MIMO technology has been considered to be a key technique for 5 G applications,since it can improve the reliability and channel capacity of MIMO systems remarkably.Compact antenna arrays with more antenna elements are desired in many application scenarios,which necessitates a smaller spacing between antenna elements.The smaller inter-element spacing leads to stronger mutual coupling,which degrades the performance of the antennas,increases the spatial correlation coefficient and deteriorates the signal-to-interference-plus-noise-ratio(SINR).Moreover,the mutual coupling can degrade the MIMO capacity and symbol error rate.Therefore,reducing mutual coupling of antenna arrays has been considered as an efficient way to enhance the performance of MIMO systems.On the other hand,there are more and more researches on metasurfaces and metamaterials in recent years.The performance of the antenna array can be effectively enhanced due to some unique properties of these new electromagnetic materials.As two-dimensional form of metamaterials,metasurfaces largely expand the range of electric parameters of the electromagnetic medium.Metasurfaces have advantages of low profile,easy processing,low loss characteristics,et cl.They have been widely used in electromagnetic wave control.In order to reduce the mutual coupling of compact MIMO antennas,this paper studied the theory and methods of mutual coupling reduction through metasurfaces.Metasurface superstrates do not take up the space between antenna elements so that the miniaturization structure can be realized.Moreover,they are easy to integrate.In this paper,we studied the decoupling theory and realization methods of metasurfaces from the perspectives of surface-wave coupling and space-wave coupling.The main contents are arranged as follows:First,the theory of surface wave reduction using metasurface is introduced.Theoretical derivation and ideal model simulation shows that when the effective electric parameters of the metamaterial superstrate have certain relationship with those of the antenna substrate,surface wave propagation can be suppressed.For example,when ?r=2.2,and the effective electric parameters of the metasurface is ?e?e=3,the surface-wave coupling of microstrip patch antenna array can be reduced.Then,a metasurface decoupling design based on space-wave coupling control is proposed.By analyzing the different coupling characteristics of E-plane and H-plane of microstrip antenna,an anisotropic metasurface structure is proposed to reduce the coupling of E-plane and H-plane by means of coupling field suppression and coupling path cancellation,respectively.The equivalent circuit and dispersion characteristics of the metasurface are analyzed.Finally,two arrays with E-plane coupling and H-plane coupling are designed and manufactured to verify the decoupling theory of the metasurface.By analyzing the coupling of dual-polarized array,we found that the free space coupling between dual-polarized patch antennas can be seen as two parts:co-polarized coupling and cross-polarized coupling.The co-polarized coupling consists of TE wave coupling and TM wave coupling.Based on these researches,this paper proposes a kind of Jerusalem-cross slot metasurface.The decoupling mechanisms for TE wave coupling and TM wave coupling are discussed based on the study of the equivalent circuit and dispersion characteristics of the metasurface.A dual-polarized patch array loaded with a metasurface superstrate is designed,and the effect of key parameters on the decoupling performance is analyzed.After proper adjustment,excellent decoupling effect can been achieved.Finally,the decoupling metasurface proposed above is extended to different MIMO antenna arrays.The decoupling designs of monopole array and cross-dipole array are proposed.In addition,to optimize the performance of the decoupling metasurface,a hybrid surface structure is proposed,which combines the reflection cancellation decoupling method with the metasurface decoupling method.Thus,the co-polarized coupling and cross-polarized coupling can be reduced simultaneously.The cross-dipole antenna arrays with multiple elements are designed and decoupled by the hybrid surface,and then the great potential of its application in large-scale MIMO array are discussed.